Ion channels are proteins that form pores in membranes of biological cells and control the flow of ions down their electrochemical gradient. They are involved in the regulation of a wide range of cellular functions in both excitable and nonexcitable cells and provide attractive therapeutic targets for the treatment of various diseases.
In the somatosensory context, CaV2.2 channels, specific cellular plasma membrane calcium channels that belong to a diverse superfamily of voltage-gated calcium channels (VGCCs), were demonstrated to play an important role in spinal nociceptive processing.
The critical role of CaV2.2 in pain processing was underlined by the clinical efficacy of the intrathecally delivered, selective CaV2.2 channel antagonist Ziconotide (SNX-111; Prialt™), a synthetic peptide derived from a ω-(omega)-conotoxin peptide (Miljanich, 2004, Curr. Med. Chem., 11(23), p. 3029-40; Staats et al., 2004, JAMA, 291(1), p. 63-70). Inthrathecal administration of Ziconotide is required in order to reach the ion channel in presynaptic terminals of sensory neurons in the spinal cord. Common side effects of Ziconotide include memory impairment, dizziness, nystagmus, speech disorder, nervousness, somnolence and abnormal gait (Rauck et al., 2009, Pain Pract., 9, p. 327-37), which have been attributed to the inhibition of CaV2.2 channels in the brain by Ziconotide.
Therefore, a demand remains for the development of orally available CaV2.2 calcium channel blockers that show the desired qualities and effectively block CaV2.2 calcium channels in the nociceptive signaling pathway.